The invention relates to head harnesses for fast attachment of a respiratory mask to the head of a user and it is particularly suitable for use by crew members of high altitude aircraft.
As the cruising altitude of passenger and business airplanes increases, it becomes more and more difficult to protect the crew members against a sudden depressurization. However, it is necessary to prevent loss of consciousness of at least one pilot upon depressurization, for him to control the aircraft for return to a safe altitude.
Respiratory mask harnesses are known (French 1,506,342 or U.S. Pat. No. 3,599,636; U.S. Pat. No. 4,437,462) which have at least one expandable strap whose ends are connected to the mask and which includes an element which is inflatable by pressurized gas for diametrically enlarging the strap to a predetermined size, sufficient for the user to place the strap around the head. Such harnesses are used on airline planes and include manually controlled means which delivers pressurized gas to the inflatable element for expanding it diametrically upon a positive action and which vents the element upon relase for causing the strap to contract, to contact the head and to maintain the mask.
In a typical embodiment, the inflating gas consists of respiratory gas which is delivered to a demand regulator carried by the mask.
Such a head harness may be stored in a box in close proximity to the seat and may be grasped by the user with one hand and donned in a time as short as some seconds. However, if depressurization occurs at a very high altitude, lack of oxygen due to exposure to vacuum during some seconds may be sufficient for causing a delayed temporary loss of consciousness after which it will be too late for the pilot to resume aircraft control.
Such a risk is avoided if the pilot, or one of the pilots, continuously dons his respiratory mask as long as the aircraft is at a high altitude, for instance beyond 10,000 meters. On the other hand permanently donning the mask applied against the face causes fatigue and strain and is detrimental to comfort. If the mask is continuously fed with oxygen, the volume of the oxygen bottle stored on-board should be higher than presently required.